The present invention relates to methods useful in sand control applications for subterranean operations. More particularly, the present invention relates to methods of creating improved circulation through stand-alone-screens used to combat particulate migration and improved placement of clean-up materials for removing drill-in filter cakes. Additionally, the methods of the present invention may be useful to repair coated screens.
Open-hole completions in soft or poorly consolidated formations require that the drill-in fluid, the sand control screen, and the cleanup system for removal of the drill-in fluid filter cake (a type of borehole filter cake) all perform together in order to provide acceptable solids control and production rates. When selecting the sand control screen for an interval, one must take into consideration the particle size distribution of any formation material that may be present in the production interval as well as the flow capacity necessary for the well to be commercially successful. Long horizontal completions often pose challenges in selecting effective sand control screens due to the wide variation in formation particle size distributions encountered across the interval.
It is well known in the subterranean well drilling and completion art that relatively fine particulate materials may be produced during the production of hydrocarbons from a well that traverses an unconsolidated or loosely consolidated formation. Numerous problems may occur as a result of the production of such particulates. For example, the particulates may lead to abrasive wear of components within the well, such as tubing, pumps and valves. In addition, the particulates may partially or fully clog the well creating the need for an expensive workover. Also, if the particulate matter is produced to the surface, it should be removed from the hydrocarbon fluids using surface processing equipment.
One method for controlling and preventing the production of such particulates is to place a gravel pack neighboring a portion of the well bore containing an unconsolidated or loosely consolidated production interval. Stand-alone-screens often are used as an alternative to gravel packs, based on the conditions present in the well bore and/or on the personal preference of the well operator. Stand-alone-screens are generally considered to be more cost-effective in terms of time and money to install over gravel packs. FIG. 1 illustrates a stand-alone-screen installed in a horizontal well bore.
A stand-alone-screen is a metal filter assembly used to support and retain the formation particulates. Stand-alone-screens may include various types of screens. Wire-wrap screens, the most common design, generally are a drilled or slotted basepipe with wire filters. In early versions, fluids flowed only through openings in the basepipe, so ribs, or rods, were added to form a small annulus for increased flow capacity and to reduce plugging. Other types of screens are pre-packed screens, which are manufactured with high-permeability resin-coated gravel between two layers of wire-wrap filter media. Premium-mesh screen designs use a specialized wire-cloth media around a wire-wrap-screen. These screens usually include a shroud with drilled holes for additional protection during installation or have openings designed to reduce erosion caused by sand grains and fine particles impacting directly on the internal filter media at high velocity. A range of sizes and screen configurations is available to suit the characteristics of the well bore, production fluid, and the formation particulates. Any of these screens may be pre-coated with a suitable coating (e.g., poly lactic acid), if desired.
Stand-alone-screens normally are used in conjunction with a concentric washpipe. The washpipe can alleviate issues, for example, when the screen has encountered an obstruction on run in. FIG. 2 illustrates a typical installation wherein a stand-alone-screen has a concentric washpipe within a subterranean formation. The washpipe may be useful to remove obstructions in the well bore and/or act as a conduit for fluid returns and carry a shifting mechanism to open or close a return port. FIG. 3 illustrates an instance where an obstruction of a bed of drill solids is present. The washpipe may be useful to provide a fluid that is able to entrain the obstruction, thus removing it from the fluid flow path. Oftentimes, the risk of obstructions in the formation is sufficient enough reason for operators to choose to use a washpipe with a stand-alone-screen, despite the many problems that are associate with such washpipes.
In many instances, the use of washpipe, especially in long horizontal wells, means the loss of valuable rig time due to make-up and break-up of the washpipe, or recovery if the washpipe is stuck. Economic considerations, along with completion efficiencies, are especially important on deepwater completions, especially in the unfortunate case of fishing if the washpipe becomes stuck. If one could avoid using washpipe, this could reduce rig time, generating significant cost savings, and also eliminating the risk of getting stuck.
Pre-coated screens that are pre-coated with various coatings have been used. These coatings are generally polyesters that eventually degrade to allow free flow through the screen and may generate an acid upon degradation. The coatings can be designed to provide certain functionalities, which may include protection of the screen during placement, and generating materials from the degradation of the coating to help with borehole cleanup. Other functionalities may also be desirable. These pre-coated screens present several potential disadvantages. For instance, the coating may be damaged when the screen is being placed downhole, which could be particularly problematic because the screen would not have a washpipe functionality. Secondly, to have enough coatings to address every potential condition that may be encountered in a subterranean operation would require the warehousing of many different kinds of screens and coating materials, which is undesirable and costly.